The present invention relates to a still picture transmission apparatus and, more particularly, to a quad-split still picture transmission apparatus in which four video pictures are compressed and transmitted.
Generally, a still picture is transmitted through a narrow band telephone transmission line so that a time period of about 42 seconds is required for transmitting a whole picture. When four different video pictures are serially transmitted, the rather long period of about 168 seconds is required for renewing the transmission corresponding to one video picture. In order to reduce the renewing period to one video picture, a quad-split still picture transmission apparatus for transmitting four compressed video pictures had been proposed in the U.S. Pat. No. 4,467,355 by the same applicant. This proposed apparatus has the advantage that the time period required for renewing each compressed video picture can be reduced to a fourth, i.e., about 10 seconds, and that four different video pictures can be monitored simultaneously.
In the proposed apparatus described above, four input terminals corresponding to four input video signals are automatically and serially switched for transmission irrespective of whether the input video signal is actually supplied or not. In other words, even if one of four input video signals is not supplied, or even if the input video signal is suddenly cut off, the transmission operation continues while there is no video information to be transmitted. Therefore, the time period of the transmission corresponding to no video information is wasted.